physics question about bullets

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Ruger480

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If you have two bullets of differing weights yet similar numbers for kinetic energy, which one will penetrate deeper?

Look at the 180 gr and the 155 grain 10mm rounds listed here.

Granted there is a difference of 5ft lbs to the heavier bullet but they are pretty close.

So, if you could tweak them a little to give the same muzzle energies, would the 180 grain penetrate further?
 
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Shape has a big effect on penetration...


But all other things being equal, the heavier round will penetrate farther. Well more or less equal, velocity will not be the same if the energy is the same with two different weight projectiles.

I made a thread on it HERE.

Heavier bullets will also out perform a lighter bullet with higher kinetic energy due to velocity.
 
momentum = mass x velocity...I was about to launch into freshman physics, but the difference is going to be much less than the variables of tissue, angle of incidence, clothing, barrel length, etc. etc.
 
To keep things simple, lets assume a non=expanding bullet, like a jacketed round nose. Now given the same kinetic energy, the bullet with the higher sectional density will penetrate further into soft media like gelatin, water, flesh, wax... higher sectional density means a heavier bullet, and given the same kinetic energy, a slower moving heavier bullet.

Against a hard target, such as glass, steel, concrete, the faster moving bullet will penetrate better... ASSUMING the bullet stays intact and non-deformed. Against hard targets, velocity is key to penetration.

This is all hypothetical, because "all things being equal" is seldom possible in the real world.

Jim
 
To keep things simple, lets assume a non=expanding bullet, like a jacketed round nose. Now given the same kinetic energy, the bullet with the higher sectional density will penetrate further into soft media like gelatin, water, flesh, wax... higher sectional density means a heavier bullet, and given the same kinetic energy, a slower moving heavier bullet.

Against a hard target, such as glass, steel, concrete, the faster moving bullet will penetrate better... ASSUMING the bullet stays intact and non-deformed. Against hard targets, velocity is key to penetration
Click to expand...

That answers my question. Thanks
 
Same depth of penetration. ft/lbs of energy=work/done

example:
lets say both projectiles were identical in weight/size/and will not deform. But one is moving 1 fps faster than the other one. The faster of the two would have more energy stored and would penetrate deeper.



example:
Take my 357 magnum carbine balistic
125grn @2250=1404.84 ft lb/energy (chronograph)
180grn @1875=1404.84 ft lb/energy (not chrono)

The 180grn would need a velocity of 1875 to equal the same energy of the 125grn. and when energy is equal than the work being done is equal.

Example: say Dad stands on a scale and it says 240 lbs. And the 45 lb son is admiring. Dad gets off the scale and son jumps on the scale and produces 240 lbs. Same energy/work produced.
 
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Yes it will as long as the bullet construction is good. The heavier bullet will perpetrate more... and perform better at distance.
 
Same depth of penetration. ft/lbs of energy=work/done

lets say both projectiles were identical in weight/size/and will not deform. But one is moving 1 fps faster than the other one. The faster of the two would have more energy stored and would penetrate deeper.

Take my 357 magnum carbine balistic
125grn @2250=1404.84 ft lb/energy (chronograph)
180grn @1875=1404.84 ft lb/energy (not chrono)

The 180grn would need a velocity of 1875 to equal the same energy of the 125grn. and when energy is equal than the work being done is equal.

Example: say Dad stands on a scale and it says 240 lbs. And the 45 lb son is admiring. Dad gets off the scale and son jumps on the scale and produces 240 lbs. Same energy/work produced.
Click to expand...

You are saying that bullet shape (and sectional density) does not matter. From your post I cannot understand why. Can you give a more clear example and explanation? Thanks in advance.
 
We have two indian spears both are identical, but A weighs 4 lbs and B weighs 8 lbs.
Drop them in the mud, both from the same elevation 10 feet and B will have more penenatration-more ft/lb of energy.
Then move spear A to higher elevations until it equals the energy or depth of spear B.

I'm not going to do the math, but A might be 25 ft higher than B. Allowing A to store its energy in form of velocity
 
You ask two questions in your thread. Your second question

"So, if you could tweak them a little to give the same muzzle energies, would the 180 grain penetrate further?"

Which I think you mean give the same "muzzle velocity"

Now if the different weight bullets have the same velocity the heavier will definately penetrate more and produce more ft/lbs of energy.
 
I'm not going to do the math, but A might be 25 ft higher than B. Allowing A to store its energy in form of velocity
Click to expand...

A will be 10 ft higher than B. But you were close :rolleyes:

You ask two questions in your thread. Your second question

"So, if you could tweak them a little to give the same muzzle energies, would the 180 grain penetrate further?"

Which I think you mean give the same "muzzle velocity"

Now if the different weight bullets have the same velocity the heavier will definately penetrate more and produce more ft/lbs of energy.
Click to expand...

I think he meant what he said, i.e. "give the same muzzle energies" (give the same kinetic energies).
 
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Generally LONGER bullets penetrate best, not always heavier. Within the same caliber longer is almost always heavier and that is why so many people misunderstand and think heavier will always out penetrate lighter. Many 9mm bullets will out penetrate 45 ACP bullets weighing much more. In this case, everything else being equal, the heavier bullets will penetrate better. But when comparing bullets of different calibers it can get real hard to predict.

Now if the different weight bullets have the same velocity the heavier will definately penetrate more and produce more ft/lbs of energy.
Click to expand...

Bullet speed, to a point is not that much of a factor in penetration. Depending on bullet construction the faster bullet will expand more, preventing penetration. Often the faster bullet will penetrate LESS than an identical bullet moving much slower. Hunters deal with this all the time. At close range a bullet might not penetrate enough to reliably take game. The same bullet at longer range, after it has slowed, will often perform much better. Even with FMJ and solids the slower bullet penetrates deeper.

The last factor is bullet construction. Which is also tied to speed.
 
At the velocities that handgun rounds fall in...

Inertia and momentum are more important than the kinetic energy.


This is in the same caliber, different calibers alter factors.

As someone mentioned, it higher sectional density. In a 9mm for example, a 124gr has a higher sectional density than a 115gr. Sectional density will change between different calibers, so direct comparisons are not always easy to do.

Hollowpoints take advantage of this property, as the bullet expands, the sectional density decreases.
 
I was was looking at ammo for the 10mm when I noticed that hornady listed their 155 gr JHP/XTP bullet at 1265 fps and 551 ft lbs of muzzle energy. Next was their 180 gr bullet also a JHP/XTP and it listed at 1180 fps and 556 ft lbs of muzzle energy. So I wondered, if one bullet was sped up a bit so that muzzle energies, not velocities, matched, which will penetrate further.

To simplify this a bit instead of using JHP bullets, let's use regular ball ammo. Exact same bullet, exact same muzzle energy (500 lbs let's say) just different weight (155 and 180 gr) and different speed. Which bullet will travel farther through ballistic gel.
 
Still... The heavier bullet.

You could even give the lighter bullet an energy advantage. In some calibers, light bullets pushed fast have higher kinetic energy... But that would not matter, the heavier bullet will travel farther.


Light bullets more readily fragment at higher velocities, which hurts penetration as mass is shed.


Handgun bullets do not travel fast enough for velocity to effect much.

Velocity matters still, as the mythbusters recently shown, you can even get a ping pong ball to make a nice clean hole through plywood if you get it moving fast enough.


You just can't get a handgun round fast enough for similar effects is soft targets. As in... it moves through so fast as to create massive shock waves in the target...
 
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A 2000 lb car is rolling at 10 mph
A 5000 lb car is rolling at 10 mph

Which would be harder to stop?

The one with the most mass.

It's mass not energy.

When I attended the North Western Traffic Institute's Accident Reconstruction Course we played with the numbers and found (per the numbers) that if you could get a bumble bee going fast enough it would stop a fright train.

We took the weight of a bumble bee and added velocity until it exceeded the KE of a 90 ton local motive at 40 mph. Once the KE of the bumble bee exceeded the KE of the engine, it should be able to stop the train.

We know that isn't gonna happen, even if you could get the bee going that fast. Numbers say it would but reality says not.
 
Problem with the bee example...


At that velocity, the bee would pass through the locomotive like it was cardboard... It wouldn't slow down the locomotive at all.


Speed up the bee even more, and it would pass through the locomotive, but the energy transfer would finally cause an effect... one that destroys the locomotive.


NASA did tests on the effects of small objects, like small bolts and nuts at high velocities, on satellites.

Get one going fast enough, and it would completely destroy the test object. Below that, you would get nice clean holes.


Speed up an object faster still... you can actually cause fusion with the lighter elements present in the object it passes through. This would create a massive explosion... basically a nuclear fusion bomb.

The speed needed is basically up in the realm of relativistic (near light) speeds.
 
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